1. Technical Field
The invention concerns a method of manufacturing internally grooved tubes for heat exchangers.
Internally grooved and lengthwise welded copper tubes are used in heat exchangers, such as e.g. air-conditioning plants, or where condensation or evaporation is required.
2. Description of the Prior Art
On the coolant side, the grooving produces better heat transfer on the inside of the tube. It is therefore possible to use smaller equipment or less coolant for the same output, or a lower flow speed of the coolant for the same output and type of construction. Such tubes are preferably manufactured by profile rolling a smooth metal tape with a rolling mill, forming the metal band into a tube and welding the lengthwise seam. The welding process may be followed by annealing.
By comparison with seamless tubes used heretofore, the lengthwise welded tubes have advantages with respect to equal wall thickness and thereby more uniform bending characteristics along the entire tube boundary. Since no lubricants are required for rolling the grooves, the internal surfaces of lengthwise welded tubes are free of lubricant residues.
The grooves rolled into the smooth metal tape extend at a 15.degree. to 45.degree. angle from the lengthwise direction of the metal tape. This provides a spin to the medium flowing inside the internally grooved metal tube, which improves the heat transfer.
A lateral force is exerted when a rolling mill produces the angled grooves on the metal tape, which tends to divert the metal tape from its direction of manufacture. The metal tape must therefore have precise lateral guidance.
However, precise guidance cannot always be guaranteed, thus unfavorably affecting the subsequent welding process. The highest demands with regard to guidance of the tape edges in the area of the welding device are particularly placed on the metal tubes in question, with a diameter of about 10 mm and a wall thickness of 0.4 mm. Beyond that, the lateral guidance can cause damage or deformation of the tape edges, which also has a deleterious effect on the quality of the welded seam.